This invention relates to the field of radio frequency (xe2x80x9cRFxe2x80x9d) transceivers and more particularly to monolithic low noise amplifier architectures used in wireless receivers that can operate at multiple frequency bands simultaneously.
Wireless communications systems have exhibited remarkable growth over the past decade. Wireless voice and data applications are being enabled by rapidly emerging wireless technologies, such as cellular telephony, personal communications systems and wireless local area networks (WLAN""s), to name a few. Digital modulation techniques, miniaturization of transceivers due to advances in monolithic integrated circuit designs and the development of high frequency, microwave and millimeter wave RF systems in both the licensed and unlicensed bands, have all contributed to improving the quality and bandwidth capacity of these system and to reducing the size and costs of the components.
These systems are having a profound effect on societies. For example, they are enabling many work forces in our global, service and information based economy to become xe2x80x9cuntetheredxe2x80x9d from their information sources and conventional wired communications mechanisms. Moreover, wireless communication systems are enabling developing countries to provide instant telephone service to new subscribers who otherwise would have to wait years for wireline access.
While many wireless applications work fairly well and have found widespread acceptance (e.g. mobile/cellular telephones), they continue to suffer from numerous drawbacks. One recognized problem in the cellular phone industry is the lack of universal standards for both signal transmission modes (analog or digital) and within digital mode the frequency bands and signal processing protocols (e.g., TDMA, CDMA, WDM, GSM, etc.). This unfortunately requires users who wish to use cell phones in different geographic areas that employ different telecommunications standards to either carry multiple telephones or to use phones designed to operate in multiple frequency modes and bands.
It would thus be highly desirable to have a receiver that can operate at multiple and discrete frequency bands. This would offer several benefits. A multi-band receiver could enable the design of a single device that can operate under multiple standards, such as GSM (with a center frequency of 900 MHz) and DECT (center frequency of 1800 MHz), thereby eliminating the need for one device per standard. While dual band receivers have been introduced that indeed increase the functionality of such communication systems, such receivers switch between two different bands and can receive only one band at a time. FIG. 1 is a schematic of such a conventional dual band architecture. As seen, an incoming signal, Vin, is received at a switch 10 (for simplicity the antenna and filter are not shown). If the signal is in a first predetermined frequency band, xcfx891, the switch moves to the top signal processing path tuned to match and amplify signals only in this band. The signal is then impedance matched and amplified at low noise amplifier (xe2x80x9cLNAxe2x80x9d) 20, mixed with local oscillator, LO1, at mixer 22, filtered at band pass filter 24 and mixed again with local oscillator, LO2, 26, until is exits as Vout for further processing (e.g. digital signal processing). Similarly, if the incoming signal is in the second predetermined frequency band, xcfx892, the switch moves to the bottom signal processing path tuned to match and amplify signals only in this band, through LNA 30, mixer 32, BPF 34 and mixer 36 and again exists as Vout. The frequency of LO1 is (xcfx891+xcfx892)/2 and the frequency of LO2 is (xcfx891xe2x88x92xcfx892)/2. While this functionality adds to a device""s versatility, such as in the case of a dual-band digital cellular phone, these receivers are more costly than single band receivers and they are not sufficient for the next-generation of multi-functional devices, such as a cell phone with a GPS receiver and a bluetooth interface.
Another problem with conventional wireless technology relates to bandwidth limitations. The diverse range of modem wireless applications demand wireless communications systems and transceivers with greater bandwidth capacity and flexibility than can be currently supplied. Increased bandwidth capacity is necessary for many wireless applications to become a reality. Wireless broadband Internet applications (e.g. browsing, e-commerce, streaming audio and video), wireless video messaging, wireless video games, and remote video monitoring are just a few examples of applications that will be delivered over the next generations of wireless networks. Conventional solid-state RF, or wireless, receiver architectures, such as superheterodyne and direct conversion receivers, accomplish high selectivity and sensitivity by designing them for narrow-band operation at a single RF frequency. Unfortunately, these modes of operation are of limited functionality because they limit the system""s available bandwidth and robustness to channel variations. On the other hand, wide-band modes of operation are more sensitive to out-of-band signals due to transistor non-linearity, which can introduce severe bottlenecks in system performance.
It would thus be highly desirable to have such a low cost, concurrent multi-band receiver. As used herein a concurrent multi-band receiver is one that can process signals at multiple and discrete frequency bands simultaneously. This would enable a single path receiver to significantly increase its bandwidth capacity (bit rate). A concurrent multi-band receiver design could also be used for supplying redundancy in mission critical data transmission application. The reliability of the received signal would be greatly increased with simultaneous transmission of the same signal in multiple bands for diversity of signal.
Using conventional receiver technology, the only way to theoretically provide concurrent multi-band functionality is to design into a receiver multiple independent signal paths with multiple sets of components (antennas, LNA""s, downconverter etc.). Such a dual-band receiver is shown schematically in FIG. 2. As shown, this design is similar to the dual band receiver in FIG. 1 without the switch 12 and separate outputs, Vout1 and Vout2. This scheme essentially equivalent to designing multiple single band receivers, each tuned to a different band and stuffed into one package. Unfortunately, this architecture significantly increases the cost, footprint and power dissipation of a receiver, and tends to make such solutions impractical, at least for commercial applications. Thus, a challenge for modern receiver design is to create concurrent multi-band functionality using as little real estate (and ideally monolithically) and as little power dissipation as possible (and perhaps no more than single band receivers), while keeping the incremental production costs above the conventional single band receiver to a minimum.
The LNA is a critical front end component of a wireless receiver. Its function is to take the relatively weak signal received at the antenna and, after filtering, amplify it with maximum power transfer and with a minimum added noise for further processing (downconversion, etc.). The maximum power transfer is achieved by designing the LNA to have an input impedance that matches a characteristic input impedance of the antenna, which is commonly 50 ohms. Thus, a true concurrent multi-band LNA, as a critical front end component of a concurrent multi-band receiver, must be capable of (1) matching the characteristic input impedance of the received signal at the antenna at the multiple frequency bands, simultaneously; (2) simultaneously amplifing the received signal(s) at each of the bands; and (3) accomplishing the above with minimum electrical noise added.
As in the case of conventional dual band receivers described above, in conventional dual-band LNA""s, for example, either one of two single-band LNA""s is selected according to the instantaneous band of operation, or two single-band LNA""s are designed to work in parallel using two separate input matching circuitry and two separate resonant loads. The former approach is non-concurrent, while the latter consumes twice as much power. The other existing approach is to use a wide-band amplifier in the front end. Unfortunately, in a wide-band LNA, strong unwanted blockers are amplified together with the desired frequency bands and significantly degrade the receiver sensitivity. Thus, a definite need exists for a concurrent multi-band LNA that eliminates these problems.
The present invention, which addresses these needs, resides in a concurrent, multi-band amplifier architecture that is capable of simultaneous operation at two or more different frequencies without dissipating twice (or more) as much power or a significant increase in cost and footprint. This concurrent operation can be used to extend the available bandwidth, provide new functionality and/or add diversity to battle channel fading. These new concurrent multi-band amplifiers, which in one aspect of the invention are LNA""S, LNA""s provide simultaneous narrow-band gain and matching at multiple frequency bands.
The present invention relates to a concurrent multi-band amplifier having an input and output. The inventive amplifier includes a three-terminal active device, such as a transistor with a characteristic transconductance, gm, disposed on a semiconductor substrate. The active device has a control input terminal, an output terminal, and a current source terminal. The amplifier also includes an input impedance matching network system, Zin, and an output load network. Zin simultaneously and independently matches the frequency-dependent input impedance of the three-terminal active device to a predetermined characteristic impedance at two or more discrete frequency bands. The output load network simultaneously provides a voltage gain, Av, to an input signal at the amplifier input at each of the two or more discrete frequency bands.
The present invention also resides in a monolithic, concurrent multi-band LNA having essentially the same three components as described above. In the LNA embodiment, however, in addition to simultaneously and independently matching the frequency-dependent input impedance of the three-terminal active device to a predetermined characteristic impedance at two or more discrete frequency bands, Zin is also designed to minimize the noise associated with the active device.
The input impedance matching network system of the multi-band LNA is defined by the equation, Zin=Z1+Z2+Z3+Z4+Z5. These five variables represent two-terminal frequency-dependent, impedance networks. In particular, Z1 is disposed between the input of the active device and ac-ground and is defined by the equation Z1=Zg+Zgs+Z""s+gmZ""sZgs., wherein Zg is a series impedance disposed between the LNA input and the control input terminal of the active device, Zgs is the impedance between the control input and current source terminals and Z""s is the sum of the impedance between the current source terminal of the active device and ac-ground, Zs, and the intrinsic current source-to-bulk impedance, Zbs.
Z2 is a second two-terminal, frequency-dependent, impedance network disposed between the input of the active device and ac-ground and defined by the equation Z2=Z""L+Zf, wherein Z""L is the sum of the load impedance between the output and ac-ground, ZL, and the intrinsic output terminal-to-bulk impedance, Zbd, and Zf is the feedback between the output terminal and control input terminal. Z3 is a third two-terminal, frequency-dependent, impedance network disposed between the input of the active device and ac-ground and defined by the equation Z3=[1+Zf/Z""L]/gmb, wherein gmb is the bulk effect transconductance.
Z4 is a fourth two-terminal, frequency-dependent, impedance network disposed between the input of the active device and ac-ground and defined by the equation This equation for Zin is a very broad implementation of the impedance matching network of the present invention.             Z      4        =                  1                              g            m                    -                      g            mb                              ·              (                              Z            f                                Z            L            xe2x80x2                          )            ·                                    Z            gs                    +                                    Z              s              xe2x80x2                        ⁢                          (                              1                +                                                      g                    m                                    ⁢                                      Z                    gs                                                              )                                                Z          gs                      ;
and Z5 is a fifth two-terminal, frequency-dependent impedance network disposed between the input of the active device and ac-ground, which is the intrinsic control terminal-to-bulk impedance, Zgb.
In a more specific embodiment of the multi-band LNA, Zf and Zgb are neglected, thereby simplifying the input impedance matching network system to Zin=Z1. Moreover, the LNA has a characteristic noise factor, F, approximated by the equation   F  ≈      1    +                            γg          d0                          Y          s                    ·              1                              g            m            2                    ⁢                                    "LeftBracketingBar"                              Z                gs                            "RightBracketingBar"                        2                              ·                                    "LeftBracketingBar"                          1              +                                                Y                  s                                ⁢                                  (                                                            Z                      gs                                        +                                          Z                      s                      xe2x80x2                                        +                                          Z                      g                                                        )                                                      "RightBracketingBar"                    2                .            
Using these formulas, Zin is matched to the predetermined characteristic impedance and F is minimized by setting Zgs+Z""s+Zg=0 for the center frequency of each of the two or more discrete frequency bands. In a specific embodiment, and as is typical in the RF industry, the predetermined characteristic impedance is equal to 50 ohms. Thus, gmZ""sZgs equals 50 ohms.
Turning to the output load network of the LNA of present invention, the voltage gain, Av, is defined by the equation Av=xe2x88x92ZL/Z""s. More particularly, the output load network is a multi-resonant load circuit disposed between the output of the three-terminal device and ac-ground that provides the voltage gain of the device at each of the discrete frequency band.
As a specific embodiment of the present invention, a monolithic, concurrent dual-band LNA having an input and output is disclosed. The input impedance matching network system, Zin, associated with the three terminal active device simultaneously and independently matches the frequency-dependent input impedance of the active device to a predetermined characteristic impedance at two discrete frequency bands, and is defined by the equation: Zin=Zg+Zgs+Z""s+gmZ""sZgs. As above, this dual band LNA sets Zg+Zgs+Z""s=0 for each of the two frequency bands, thereby making gm Z""sZgs equal to the predetermined characteristic impedance, which preferably is 50 ohms.
As one implementation of this dual band topology, Zg is a parallel LC network wire bonded to the input of the three terminal device and Z""s is an inductor. Moreover, the LNA includes an output load network, ZL, that simultaneously provides a voltage gain, Av, to an input signal at the LNA input at each of the two discrete frequency bands. This load network, ZL, is a series LC branch in parallel with a parallel LC tank.
The inventors have designed a concurrent dual band CMOS LNA, having an input and an output that operates simultaneously at 2.45 GHz and 5.25 GHz center frequency bands. The input impedance network, Zin, simultaneously and independently matches the frequency-dependent input impedance of the transistor to a 50 ohm characteristic impedance at center frequencies of 2.45 GHz and 5.25 GHz, and is defined by the equations: Zin=Zg+Zgs+Z""s+gmZ""sZgs,=50 xcexa9 and Zg+Zgs+Z""s=0. In particular, Zg is an input parallel resonator having a capacitor in parallel with an inductor, disposed between the LNA input and gate and with a wire bonded to the gate, Zgs is the impedance between the gate and source, and Z""s is an inductor disposed between the source and AC ground. The input parallel resonator is an approximately 0.9 pF capacitor in parallel with an approximately 2.7 nH inductor with the wire boding having an approximate inductance value of 3 nH, Z""s is an approximately 0.7 nH inductor, the series LC branch circuit is an approximately 240 fF capacitor in series with an approximately 9.8 nH inductor, and the parallel LC tank circuit is an approximately 2.3 nH inductor in parallel with the inherent parasitic inductance of the active device. Moreover, the output load network, ZL, that simultaneously provides a voltage gain, Av, to an input signal at the LNA input at the 2.45 GHz and 5.25 GHz center frequencies, wherein the output load network, ZL, is a series LC branch circuit, in parallel with a parallel LC tank circuit.
A method of concurrently amplifying a multi-band input signal on a semiconductor substrate having a monolithic, three-terminal active device is also described. The method includes simultaneously and independently matching the frequency dependent, input impedance of the three terminal active device to a predetermined characteristic input impedance at two or more discrete frequency bands, and simultaneously providing a voltage gain to the input signal at each of the two or more discrete frequency bands. The method further simultaneously minimizes the noise associated with of the impedance-matched input signal at each of the two or more discrete frequency bands.
Other features and advantages of the present invention should become more apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.